6019( 26) - 12/19/95 17:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6019 Version: 26 Check-in Date: ********** 1.Proposal Title: SUPERSONIC VELOCITY DISPERSION IN DWARF NOVA ACCRETION DISKS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Keith Horne University of St. Andrews CoI: Thomas Marsh University of Southhampton N CoI: Fuhua Cheng University of Maryland N CoI: Ivan Hubeny NASA Goddard Space Flight Center N ------------------------------------------------------------------------------------ 6. Abstract In a Cycle 1 HST study of eclipses of the dwarf nova OY Car in quiescence, we discovered strong Fe II absorption features that appear to form in the upper atmosphere (chromosphere) of the accretion disk along the line of sight to the white dwarf. Analysis of the spectrum allowed us to determine the temperature, density, column density, and velocity dispersion of the absorbing gas. The velocity dispersion is Mach 6, thought to be impossible for hydrodynamic turbulence. Furthermore, the column density is so high that the gas cannot be supported so far above the disk plane by thermal pressure alone. This is an exciting HST discovery that may be interpreted as evidence that magnetic turbulence supports the vertical structure of quiescent accretion disks. Our previous HST observations of OY Car were confined to a narrow range of phases around the eclipse. We will now obtain FOS and GHRS spectra of OY Car around complete binary orbits to map the supersonic velocity profile and other characteristics of the absorbing gas as functions of azimuth around the rim of the disk. This will establish whether the supersonic dispersion is due to turbulence or bulk motions, and whether it is intrinsic to the disk or induced by impact of the gas stream. We will also obtain FOS coverage of 3 additional short-period eclipsing dwarf novae to determine if the phenomenon is a widespread characteristic of quiescent accretion disks. ------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 2] Observations Description ------------------------ OY Car is in the continuous viewing zone. Thus in 4 96-minute HST orbits we can acquire the target and then observe continuously for 3.9 91-minute binary orbits, including 4 eclipses. We start with FOS/BL/G160L, as used in our earlier study of OY Car eclipses. This covers 1150 to 2500 Angstroms with a FWHM resolution of 9 Angstrom (1800 kms) in 1st order, plus simultaneous wide- band 3400 Angstrom photometry in order 0. We will use the RAPID mode with SUB- STEPS=2 and STEP-TIME=4s to record the eclipse shapes and orbital light curves at all uv wavelengths. The G160L coverage of 1.3 binary orbits should start at phase 0.8-0.9 in order to include 2 consecutive eclipses. The full binary orbit probes the azimuthal structure of the disk, while the eclipses serve to separate the white dwarf light from the background spectrum arising from the disk and other parts of the system. Our analysis of these data will yield the temperature of the white dwarf, plus the temperature, density, column density, and velocity dispersion of the absorbing gas along the line of sight at every azimuth around the rim of the disk. Following this we will attempt to confirm the results by extending the wavelength coverage and increasing the resolution by using FOS/RD with G190H, G270H, and G400H exposures lasting 0.3, 0.3, and 1.0 binary orbits respectively. The G190H and G270H exposures will cover out-of -eclipse phases, while the G400H exposure covers a full binary orbit including 1 eclipse. These spectra will record MgI, CaII, and Balmer emission lines from the disk chromosphere, which we believe to be the same gas that produces the FeII absorption features when backlighted by the white dwarf. Following the FOS observations we switch to the higher-resolution GHRS/G270M mode, with a FWHM resolution of 15 kms in a 40 Angstrom spectral window near 2000 Angstrom, and immediately observe OY Car again for 1.0 binary orbits including 1 eclipse. The GHRS data should resolve individual absorption lines and directly verify whether the distinctive pattern of Fe II absorptions in the FOS spectra is caused by a supersonic velocity dispersion. The limited spectral coverage of the GHRS data make it unsuitable on its own for determining the white dwarf temperature or physical conditions in the absorbing gas, but its high spectral resolution should allow a direct mapping of the radial velocity distribution (e.g. both dispersion and shift) in the absorbing gas at different azimuths around the disk. By combining the GHRS observations with the FOS observations obtained on the previous binary orbit we should have the information needed to determine both the physical conditions and the radial velocity distribution of the absorbing gas as functions of azimuth around the disk. The GHRS data should also allow us to distinguish photospheric absorption features intrinsic to the white dwarf (if these features are present at solar abundance) from those due to the intervening disk material, and hence to measure and rotation rate, radial velocity curve, and chemical abundances on the surface of the white dwarf. Finally, we will use FOS/BL/G160L to observe 1 eclipse each of the dwarf novae Z Cha, V2051 Oph, and WZ Sge. For each object we will use 1 HST orbit for target acquisition, and then a second HST orbit to cover the eclipse. Time not used for target acquisition in the first HST orbit will be used to take spectra of the target at a binary phase away from the eclipse. Our exposure times are dictated by the need to cover specific binary phase ranges rather than by S/N requirements. For OY Car we need 2 full 1.5h binary orbits, plus 2 target acquisitions, a total of 4 HST orbits. For each of the other 3 targets we need 2 HST orbits, one to acquire the target and a second to observe an eclipse (requiring 20- 25 minutes). Scheduling becomes nearly impossible if the target acquisition and eclipse observation are packed into one orbit. Thus the total time is 4 + 3 * 2 = 10 HST orbits. Real Time Justification ----------------------- We need to observe OY Car in the continuous viewing zone in order to obtain uninterrupted observations covering full 1.5h binary orbit cycles. We need time -critical observations so that our HST observations catch eclipses. The binary ephemerides of the objects are well known, and so we can predict beforehand exactly when these eclipses occur. We used this mode with mixed success in our previous HST study of OY Car, and the bugs in the ground system software that were found as a result of these earlier observations have now been corrected so that we should have no difficulty in making these time-critical observations catch the intended eclipses. We will attempt to obtain contemporaneous or if possible simultaneous ground-based observations (CCD light curves and/or time- resolved spectroscopy) of the objects under study by using e-mail to contact potential observers once the HST observing schedule is known. The network of observers working on cataclysmic variables is large enough that we find this method is usually successful even given the vagarities of HST scheduling. For this reason we would appreciate being notified whenever the dates of the observations are scheduled, or when their scheduled dates are changed. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Keith Horne,*Physics & Astronomy,*North Haugh,*St. Andrews, KY16 9SS,*Scotland, U.K. Ship Via: UPS Email: kdh1@st-and.ac.uk , ------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 OY-CAR STAR, INTERACTING RA=10H 6M 22.47S +/- 0.4", DEC= 2000 V = 15.3+/-0.5 BINARY, DWARF NOVA -70D 14' 4.8" +/- 0.4", PLATE- E(B-V) = 0.0+/-0.05 ID=0196 B-V = 0.0+/-0.2 U-B = -1.0+/-0.3 Comments: ECLIPSING BINARY, RAPID VARIABLE 2 Z-CHA STAR, INTERACTING RA=8H 7M 28.13S +/- 0.4", DEC=- 2000 V = 15.3 BINARY, DWARF NOVA 76D 32' 1.1" +/- 0.4", PLATE- E(B-V) = 0.0+/-0.05 ID=00RH B-V = 0.0+/-0.2 U-B = -1.0+/-0.3 Comments: ECLIPSING BINARY, RAPID VARIABLE 3 V2051-OPH STAR, INTERACTING RA=17H 8M 19.10S +/- 0.4", DEC= 2000 V = 15.0 BINARY, DWARF NOVA -25D 48' 30.8" +/- 0.4", PLATE- E(B-V) = 0.0+/-0.05 ID=067P B-V = 0.0+/-0.2 U-B = -1.0+/-0.3 Comments: ECLIPSING BINARY, RAPID VARIABLE 4 WZ-SGE STAR, INTERACTING RA=20H 7M 36.41S +/- 0.4", 2000 V = 15.3 BINARY, DWARF NOVA DEC=+17D 42' 15.4" +/- 0.4", E(B-V) = 0.0+/-0.05 PLATE-ID=02UQ B-V = 0.0+/-0.2 U-B = -1.0+/-0.3 Comments: ECLIPSING BINARY, RAPID VARIABLE 6019( 26) - 12/19/95 17:36 - [ 5] Visit: 01 Visit Requirements: CVZ PERIOD 0.0631209239D AND ZERO-PHASE JD2450099.998259 On Hold Comments: Additional Comments: OY Car This table shows the binary phase ranges we want to cover: EXP DET GRAT START DUR STOP 4 FOS/BL G160L 0.8-0.9 1.3 1.1-1.2 5 FOS/RD G190H 1.1- 1.2 0.3 1.4-1.5 6 FOS/RD G270H 1.4-1.5 0.3 1.7-1.8 7 FOS/RD G400H 1.7-1.8 1.0 2.7-2.8 8 GHRS G270M 1.7-1.8 1.0 3.7-3.8 If scheduling permits, extend coverage at beginning with G160L or at the end to increase the total exposure time on GHRS. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OY-CAR S/C DATA NONE 1 1S PHASE .08 TO .92 SEQ 1-2 NON-INT Comments: Target acqusition cannot be done during eclipse. Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 2 OY-CAR FOS/BL ACQ/BIN 4.3 MIRROR 1 10S ONBOARD ACQ FOR 5-12 ARY ------------------------------------------------------------------------------------------------------------------------------------ 5 OY-CAR S/C DATA NONE 1 1S PHASE 0.8 TO 0.9 SEQ 5-6 NON-INT Comments: Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 6 OY-CAR FOS/BL RAPID 1.0- G160L READ-TIME=4,SUB 1 118M PAIR-A -STEP=2,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 7 OY-CAR FOS/RD ACCUM 1.0 G190H 1 1S PHASE 0.1 TO 0.8 SEQ 7-8 NON-INT Comments: Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. Cannot use S/C exposure here because FOS side switch would occur between this exposure and the next in that case. ------------------------------------------------------------------------------------------------------------------------------------ 8 OY-CAR FOS/RD RAPID 1.0 G190H READ-TIME=4,SUB 1 27M -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 9 OY-CAR FOS/RD RAPID 1.0 G270H READ-TIME=4,SUB 1 27M -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 10 OY-CAR FOS/RD RAPID 1.0 G400H READ-TIME=4,SUB 1 91M -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 OY-CAR S/C DATA NONE 1 1S PHASE 0.1 TO 0.9 SEQ 11-12 NON-INT Comments: Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 12 OY-CAR HRS ACCUM 2.0 G270M 2200 STEP- 200 27.2S TIME=0.2,STEP- PATT=5,COMB=FOU R,FP- SPLIT=NO,DOPPLE Comments: R=ON ------------------------------------------------------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 7] Visit: 02 Visit Requirements: PERIOD 0.07449935704D AND ZERO-PHASE JD2449970.97329 On Hold Comments: Additional Comments: Z Cha Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 Z-CHA S/C DATA NONE 1 1S PHASE .08 TO .92 SEQ 1-5 NON-INT Comments: Target acqusition cannot be done during eclipse. Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 2 Z-CHA FOS/RD ACQ/BIN 4.3 MIRROR 1 3S ONBOARD ACQ FOR 5-6 ARY ------------------------------------------------------------------------------------------------------------------------------------ 5 Z-CHA FOS/RD RAPID 1.0 G400H READ-TIME=4,SUB 1 796S -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 6 Z-CHA FOS/BL RAPID 1.0- G160L READ-TIME=4,SUB 1 2372S NO SPLIT PHASE 0.75 TO 0.85 PAIR-A -STEP=2,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 8] Visit: 03 Visit Requirements: PERIOD 0.062427887D AND ZERO-PHASE JD2444043.68019 On Hold Comments: Additional Comments: V2051 Oph Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 V2051-OPH S/C DATA NONE 1 1S PHASE .08 TO .92 SEQ 1-5 NON-INT Comments: Target acqusition cannot be done during eclipse. Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 2 V2051-OPH FOS/RD ACQ/BIN 4.3 MIRROR 1 2S ONBOARD ACQ FOR 5-6 ARY ------------------------------------------------------------------------------------------------------------------------------------ 5 V2051-OPH FOS/RD RAPID 1.0 G400H READ-TIME=4,SUB 1 452S -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 6 V2051-OPH FOS/BL RAPID 1.0- G160L READ-TIME=4,SUB 1 39M NO SPLIT PHASE 0.7 TO 0.9 PAIR-A -STEP=2,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 9] Visit: 04 Visit Requirements: PERIOD 0.0566878455D AND ZERO-PHASE JD2437547.72845 On Hold Comments: Additional Comments: WZ Sge Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WZ-SGE S/C DATA NONE 1 1S PHASE .08 TO .92 SEQ 1-5 NON-INT Comments: Target acqusition cannot be done during eclipse. Phase critical observation is longer than period. Ground system does not support this. Put PHASE on this exposure and link it via SEQ NON-INT to real science to work around ground system limitation. ------------------------------------------------------------------------------------------------------------------------------------ 2 WZ-SGE FOS/RD ACQ/BIN 4.3 MIRROR 1 3S ONBOARD ACQ FOR 5-6 ARY ------------------------------------------------------------------------------------------------------------------------------------ 5 WZ-SGE FOS/RD RAPID 1.0 G400H READ-TIME=4,SUB 1 7M -STEP=2 ------------------------------------------------------------------------------------------------------------------------------------ 6 WZ-SGE FOS/BL RAPID 1.0- G160L READ-TIME=4,SUB 1 2312S NO SPLIT PHASE 0.65 TO 0.9 PAIR-A -STEP=2,STEP- PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6019( 26) - 12/19/95 17:36 - [ 10] Summary Form for Proposal 6019 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations S/C FOS/BL FOS/RD HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes DATA ACQ/BINARY RAPID ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters READ-TIME=4 SUB-STEP=2 STEP-PATT=SINGLE DOPPLER=ON ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ PERIOD 0.0631209239D AND ZERO-PHASE JD2450099.998259 PHASE .08 TO .92 SEQ 1-2 NON-INT ONBOARD ACQ FOR 5-12 PHASE 0.8 TO 0.9 SEQ 5-6 NON-INT PHASE 0.1 TO 0.8 SEQ 7-8 NON-INT PHASE 0.1 TO 0.9 SEQ 11-12 NON-INT PERIOD 0.07449935704D AND ZERO-PHASE JD2449970.97329 PHASE .08 TO .92 SEQ 1-5 NON-INT ONBOARD ACQ FOR 5-6 NO SPLIT PHASE 0.75 TO 0.85 PERIOD 0.062427887D AND ZERO-PHASE JD2444043.68019 NO SPLIT PHASE 0.7 TO 0.9 PERIOD 0.0566878455D AND ZERO-PHASE JD2437547.72845 NO SPLIT PHASE 0.65 TO 0.9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L G190H G270H G400H G270M ------------------------------------------------------------------------------------------------------------------------------------ Target Names OY-CAR Z-CHA V2051-OPH WZ-SGE ------------------------------------------------------------------------------------------------------------------------------------